The governor's approval of the bill was in doubt until the last minute, when he signed it as part of a series of measures that he said would protect

children and strengthen families. The video game industry, which has sales of more than $7 billion a year and is largely based in California, lobbied heavily against the bill and vowed to challenge it in court, saying it violated the First Amendment's guarantees of free speech.

Mr. Schwarzenegger also signed a bill on Friday prohibiting the use of dietary supplements and steroid substitutes by high school athletes. Earlier this year, he severed a financial relationship with two fitness magazines that get a large share of their advertising from the makers of such supplements. The governor, a former champion bodybuilder, vetoed a similar bill last year, prompting accusations of a conflict of interest.

Under the measure Mr. Schwarzenegger signed Friday, high school athletes must attest in writing that they are not taking performance-enhancing substances banned by the United States Anti-Doping Agency, including synephrine, ephedra and DHEA. They can be expelled for violating the ban.

The law also requires coaches to attend a training class on how to spot the use of illegal substances and to warn students about their dangers.

The video game measure is similar to bills passed recently in Illinois and Michigan but is expected to have far broader impact because of the size of the California market and the state's role in blazing national trails on social issues.

The bill bans the sale or rental to those under 18 of any video games that "depict serious injury to human beings in a manner that is especially heinous, atrocious or cruel." Violations carry a fine of up to $1,000.

The bill passed with wide bipartisan majorities and was endorsed by a broad range of family and medical associations, the National Association for the Advancement of Colored People and the California Parent-Teacher Association.

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"Many of these games are made for adults, and choosing games that are appropriate for kids should be a decision made by their parents," Mr. Schwarzenegger said in a statement.

The issue of violence in video games is not new, with numerous games that arm players with fantastically powerful weapons used to kill or dismember their enemies.

But the issue erupted onto the national scene in recent years with the popularity of the Grand Theft Auto franchise. The games, made by Take-Two Interactive, reward a player for undertaking various criminal pursuits, including shooting rivals and stealing cars.

The games are rated "M," for mature, meaning they are intended for players 17 and older. The latest version of the game, Grand Theft Auto: San Andreas, caused a particular uproar because it included a sexually explicit animated scene that had not been disclosed to the Entertainment Software Rating Board, which rates video games. Its only rating higher than "M" is "AO" for "Adults Only," for players 18 and over. The law does not refer to the existing rating system, but James Steyer, founder of Common Sense Media, a group that pushed for the law, said video games affected by the law would be those rated "M" or higher.

The bill's sponsor is Assemblyman Leland Yee, a child psychologist and a former school administrator. Mr. Yee, a Democrat from San Francisco, said he expected the measure to survive court challenge because it was carefully written to outlaw the sale or rental of such games to minors, not to punish the writers or publishers of the games.

He said growing scientific evidence linked the playing of the games by impressionable teenagers and preteenagers to acts of violence or hostile attitudes toward girls and women. "Study upon study shows that these ultraviolent games have harmful effects on our children," Mr. Yee said. Douglas Lowenstein, president of the Entertainment Software Association, the main trade group for the video game industry, said in a statement that he expected the courts to declare the California law invalid, as they have in other jurisdictions.

"We are disappointed that politicians of both parties chose to toss overboard the First Amendment and free artistic and creative expression in favor of political expediency," Mr. Lowenstein said.

Matt Richtel contributed reporting from San Francisco for this article.

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A version of this article appears in print on October 8, 2005, on Page A00011 of the National edition with the headline: Bill Is Signed To Restrict Video Games In California. Order Reprints|Today's Paper|Subscribe